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Abstract Powdery mildews (Erysiphaceae) are obligate fungal pathogens that infect over 10,000 plant taxa worldwide. Oaks (Quercusspp.) are a particularly important group of hosts due to their ecological and economic value. Recent molecular work has revealed that species infecting North American oaks are more diverse and host-specific than previously recognized. Here, we describeErysiphe quercus-palustrissp. nov., collected onQuercus palustrisin North Carolina, and clarify the placement of the previously described speciesE. abbreviata. Phylogenetic analyses support the separation of the new species from the main “North American”Erysipheclade whose species are typically characterized by aerial hyphae, a feature absent inE. quercus-palustris. This study contributes to the growing evidence of cryptic diversity within oak-infecting powdery mildews and underscores the importance of continued taxonomic and phylogenetic research on pathogens of ecologically important hosts. 

ABSTRACT The powdery mildew fungusErysiphe quercicola(Erysiphaceae) has a complex taxonomic history that has long complicated assessments of its geographic distribution and host associations. Although knowledge of the global host range of this species has expanded substantially over the past two decades, sequencing‐confirmed records from North America remain scarce, and despite its recognition as an introduced pathogen, the timing of introduction and the geographic extent and host range ofE. quercicolain the United States are poorly understood. In this study, herbarium specimens ofE. quercicolafrom North America, spanning both historical and contemporary collections, were examined using molecular phylogenetic approaches. Specimens collected from multipleQuercusspecies across several regions of the United States, as well as from related hosts within theFagaceae, were evaluated. Sequence data confirm the presence ofE. quercicolain North America onQuercusspecies based on herbarium specimens collected as early as 1944, as well as on mango (Mangifera indica;Anacardiaceae) in Florida from material collected in 1935. These records raise the possibility of historical introduction pathways associated with cultivated hosts, potentially from the horticulturally important mango tree (M. indica); however, additional multilocus phylogenetic analyses and host range inoculation experiments will be required to determine whether powdery mildew populations infecting mango andQuercusin North America represent the same lineage. Additional sequencing‐confirmed records document the species on multiple native oak species representing different sections ofQuercusincludingQ. bicolor,Q. gambelii,Q. garryana,Q. geminata,Q. kelloggii,Quercus × jolonensisandQ. macrocarpaas well as onNotholithocarpus densiflorus. Together, these findings clarify the long‐term presence ofE. quercicolain the United States, expand knowledge of its North American host range, and demonstrate the value of herbaria for reconstructing the invasion history of forest pathogens. 

ABSTRACT Aesculusis a genus of woody plant species that contains multiple ecologically and ornamentally important species. Powdery mildew is common on this host genus and is particularly virulent on the economically significant horse chestnut,Aesculus hippocastanum. Previously, allErysiphespecies found onAesculusspp. were identified asErysiphe flexuosa. Recent genomic research has indicated that powdery mildew species frequently show a high degree of host specificity which was not captured by traditional morphological approaches. As such, we proceeded to collect and sequence multiple regions of the powdery mildew genome to determine the causal agents of disease on differentAesculusspp. The results of our multilocus phylogenetic analyses revealed the existence of a genetically distinct species, which has been found only onAesculusspp. native to North America.Erysiphe aesculi‐sylvaticaesp. nov. is proposed for this cryptic species. In the past 25 years, there have been multiple reports of anE. flexuosaepidemic onAesculus hippocastanumin Europe, whileE. aesculi‐sylvaticaehas yet to be identified outside of the United States. The discovery of this new cryptic powdery mildew species as well as analysis of additional sequences from collections ofE. flexuosafrom North America, including from the type specimen collected in 1872, are discussed in detail with an emphasis on the implications for the co‐evolution, worldwide spread, and invasion dynamics of these powdery mildews. Future research should continue to collect and sequence powdery mildews on differentAesculusspp. to better understand the diversity and spread of these economically important pathogens. 

Summary Powdery mildew is an economically important disease caused byc. 1000 different fungal species.Erysiphe vacciniiis an emerging powdery mildew species that is impacting the blueberry industry. Once confined to North America,E. vacciniiis now spreading rapidly across major blueberry‐growing regions, including China, Morocco, Mexico, and the USA, threatening millions in losses.This study documents its recent global spread by analyzing both herbarium specimens, some over 150‐yr‐old, and fresh samples collected world‐wide.Our findings were integrated into a ‘living phylogeny’ via T‐BAS to simplify pathogen identification and enable rapid responses to new outbreaks. We identified 50 haplotypes, two primary introductions world‐wide, and revealed a shift from a generalist to a specialist pathogen.This research provides insights into the complexities of host specialization and highlights the need to address this emerging global threat to blueberry production. 

ABSTRACT Erysiphespecies infecting oaks in North America are common and widespread, but compared to Asia and Europe, the taxonomy and phylogeny of North American species is unknown. The present study addresses this dispairity. Comprehensive multilocus phylogenetic analyses, includingCAM,GAPDH,GS, ITS,RPB2andTUB, revealed a high degree of co‐evolution between North American oaks and theErysiphespp. that infect them. A concatenated multilocus tree and individual trees based on single loci revealed many highly supported species clades. The clades are formally named to conform with the current taxonomic classification. Available names, such asE. abbreviata,E. calocladophoraandE. extensa, are associated with corresponding clades, and are newly circumscribed supported by ex‐type sequences or, if not available, by the designation of epitypes with ex‐epitype sequences.Erysiphe densissimais reintroduced for a clade that corresponds to the old name ‘E. extensavar.curta’. Eight new species are described, includingErysiphe carolinensis,E. gambelii,E. occidentalis,E. phellos,E. pseudoextensa,E. quercophila,E. quercus‐laurifoliaeandE. schweinitziana. A new diagnostically and taxonomically relevant trait associated with the anamorphs of North AmericanErysiphespecies on oaks has been assssed. This is a special conidiophore‐like lateral outgrowth of the superficial hyphae, comparable to ‘aerial hyphae,’ which are also known for species of the powdery mildew genusCystothecawhich also infectQuercusspecies. 

Powdery mildew is a persistent disease affecting the cultivation ofRosa, a genus of substantial horticultural and economic value worldwide. Despite more than a century of study, the true diversity of powdery mildews infecting roses has remained unclear, largely due to the long-standing and overly broad application of the namePodosphaera pannosa. To reassess this system, we conducted an extensive investigation of powdery mildew specimens infectingRosa. A total of 112 collections were examined, including recently gathered material from 23 provinces, historical types, representative specimens from the Herbarium Mycologicum Academiae Sinicae (HMAS), China, and a neotype specimen from Germany. Morphological observations combined with phylogenetic analyses (ITS, 28S, and IGS rDNA) resolved several long-standing taxonomic problems and revealed unexpected diversity within therosepowdery mildew complex. Molecular data fromErysiphe rosaeprovide the first phylogenetic evidence supporting the synonymy ofMedusosphaerawithErysiphe.Sphaerotheca rosae, previously treated as a synonym ofP. pannosa, is reinstated as a distinct species asPodosphaera rosaecomb. nov., and a previously unrecognized lineage is described asPodosphaera rosae-xanthinaesp. nov. In addition, earlier varieties ofE. simulansare shown to lack diagnostic morphological or genetic characters and are no longer supported. Taken together, these results demonstrate that powdery mildews onRosarepresent a complex of five species across two genera, structured by host phylogeny. Clear patterns of host preference and distribution indicate a history of co-evolution and ecological differentiation driven by host availability. This study fundamentally revises our understanding of rose powdery mildews, revealing a level of taxonomic and evolutionary complexity much greater than previously recognized and highlightingRosaas a key host lineage in the diversification of theErysiphaceae. 

Botanical gardens host diverse plant assemblages that provide valuable opportunities to study fungal biodiversity and plant–fungal interactions. Powdery mildews (Erysiphaceae) are common pathogens in these settings, yet little is known about how they co‐occur with culturable fungi present on infected leaves. To document fungi recovered from infected tissue, we surveyed powdery mildew infections at the JC Raulston Arboretum, which is part of North Carolina State University. We identified the powdery mildew species present and the fungi that could be cultured from the infected phyllosphere. Eighteen powdery mildew species representing three genera were documented and confirmed through morphological and molecular methods. Using a dilution‐to‐extinction culturing approach, we recovered 147 isolates corresponding to 57 fungal species across 36 genera. Several genera includingAspergillusandCladosporiumwere repeatedly recovered from powdery mildew‐infected leaves, and six isolates represent potentially novel lineages. Several of these genera have previously been shown to possess biological control potential against powdery mildew. These findings demonstrate that botanical gardens harbor rich, underexplored fungal diversity and that powdery mildew–infected tissues provide access to a broad community of co‐occurring fungi. Our results highlight the potential of culture‐based surveys in botanical gardens to uncover novel fungal taxa and identify candidate biological control agents for powdery mildew management.